Work in the last year (2/79-3/80) has dealt with the turnover of elastin in murine lung exposed to ozone (1.5 ppm for 4 day periods at 2-3 month intervals). Elastin was labelled in lung following injection with 14C-lysine. This allowed estimation of desmosine specific radioactivity as an indicator of elastin turnover. Desmosine is a cross-linking amino acid derived from lysine. Following two exposures to ozone, there is little indication of significant turnover of desmosine, although signs of elastolytic damage (visualized histochemically) were evident. In addition, estimates of elastin turnover in quail lung (measured by the same procedures) indicate relatively little turnover of elastin (desmosine) in aorta or lung from this species. Less than 5 percent of the variation in desmosine or lysine specific activity in elastin was related to changes in time in experiments carried out over a year period. Further, data were obtained for a soluble form of elastin that is larger in molecular weight than tropoelastin (95,000 vs. 72,000 daltons). This form of elastin either represents a proform to tropelastin or a tropoelastin-protein complex. Current work is directed at determining its role in elastin fiber assembly.